Mitochondria generate the bulk of cellular energy through electron transport and oxidative phosphorylation. They are semiautonomous organelles in that they contain their own DNA genomes (mtDNA) which are replicated, transcribed and translationally expressed within the mitochondrial matrix. However, the coding capacity of mtDNA is limited to 13 protein subunits of the respiratory complexes, and the rRNAs and tRNAs required for their translation. Thus, the nuclear genome, provides nearly all of the constituents needed for mitochondrial functions including the maintenance and expression of mtDNA. This arrangement necessitates the interplay of nuclear and mitochondrial genetic systems in meeting cellular energy demands. Both nuclear and mitochondrial genetic lesions, affecting the energy transducing systems of mitochondria, lead to a wide range of human diseases including various forms of myopathy, cardiomyopathy and central nervous system defects. The overall goal of this proposal is to investigate nuclear regulatory mechanisms that control respiratory chain expression. The main focus is on utilizing biochemical, molecular and genetic approaches to understand the biological functions of nuclear regulatory proteins (NRF-1 and NRF-2), that have been implicated in the expression of the mitochondrial respiratory apparatus. The specific aims are: 1) To characterize newly-constructed transgenic mice that have a targeted disruption of the NRF-1 gene. This genetic approach will provide insights into the in vivo functions of NRF-1. 2) To explore the regulatory role of NRF phosphorylation in the expression of the respiratory chain. Phosphorylation of NRF-1 has been associated with increased respiration upon entry to the cell cycle. 3) To investigate the participation of the PGC-1 co-activator in the expression of NRF- dependent genes. PGC-1 is a probable link between adaptive thermogenesis and mitochondrial biogenesis. 4) To study the transcriptional mechanisms of NRF and mRNA induction upon electrical stimulation of neonatal cardiomyocytes. 5) To explore the role of newly discovered protein-protein interactions in NRF function. Completion of these aims will facilitate the understanding of the mechanisms of nucleomitochondrial interaction in mammalian cells.